1. Field of the Invention
The present invention relates to a hydraulically damped mounting device. Such a device usually has a pair of chambers for hydraulic fluid, as a pair of chambers for hydraulic fluid, connected by suitable passageway, and damping is achieved due to the flow of fluid through that passageway.
2. Summary of the Prior Art
EP-A-0115417 and GB-A-2282430 discussed a type of hydraulically damped mounting devices for damping vibration between two parts of a piece of machinery, e.g. a car engine and a chassis, referred to as a xe2x80x9ccup and bossxe2x80x9d type of mounting device, in which a xe2x80x9cbossxe2x80x9d, forming one anchor part to which one of the pieces of machinery was connected, was itself connected via a deformable (normally resilient) wall to the mouth of a xe2x80x9ccupxe2x80x9d, which was attached to the other piece of machinery and formed another anchor part. The cup and the resilient wall then defined a working chamber for hydraulic fluid, which was connected to a compensation chamber by a passageway (usually elongate) which provided the damping orifice. The compensation chamber was separated from the working chamber by a rigid partition, and a flexible diaphragm was in direct contact with the liquid and, together with the partition formed a gas pocket.
In the hydraulically damped mounting devices disclosed in the specifications discussed above, there was a single passageway. It is also known, from other hydraulically damped mounting devices, to provide a plurality of independent passageways linking the chambers for hydraulic fluid.
FIG. 1 of the accompanying drawings shows one example of a xe2x80x9ccup and bossxe2x80x9d type of mounting device which has been disclosed in our GB-A-2282430. The mounting device is for damping vibration between two parts of a structure (not shown), and has a boss 1 connected via a fixing bolt 2 to one of the parts of the structure, and the other part of the structure is connected to a generally U-shaped cup 4. A resilient spring 5 of e.g. rubber interconnects the boss 1 and the cup 4 and extends across the mouth of the cup 4. Thus, a working chamber B is defined within the mount, bounded by the resilient spring 5 and the partition 7.
The interior of the partition 7 defines a convoluted passageway 9 which is connected to the working chamber 8 via an opening 10 and is also connected via an opening 11 to a compensation chamber 12. Thus, when the boss 1 vibrates relative to the cup 4 (in the vertical direction in FIG. 1), the volume of the working chamber 8 will change, and hydraulic fluid in that working chamber 8 will be forced through the passageway 9 into, or out of, the compensation chamber 12. This fluid movement causes damping. The volume of the compensation chamber 12 needs to change in response to such fluid movement, and therefore the compensation chamber 12 is bounded by a flexible wall 13.
In use, the force received by the mounting device is principally parallel to the fixing bolt 2, and this direction defines an axis of the boss 1.
The above structure is generally similar to that described in EP-A-0115417, and the manner of operation is similar. In EP-A-0115417, the partition supported a diaphragm which acted as a boundary between fluid in the working chamber and a gas pocket. In the arrangement shown as FIG. 1, there is an annular diaphragm 50 which is convoluted. That diaphragm 50 is held on the partition 7 by an upper snubber plate 22, that snubber plate 22 is held in pace by a ring 40, which is clamped to the partition 7 and to the cup 4, by a clamping ring 41. The resilient spring 5 is also connected to the ring 40. The upper snubber plate 22 has openings 21 which permits fluid in the working chamber 8 to contact the diaphragm 50.
In the arrangement shown in FIG. 1, the passageway 9 is in the form of a spiral, and the internal dimensions of that spiral are uniform.
Under normal operation, the resilient wall is sufficiently strong to resist the forces that will be applied to it due to movement of e.g. the engine relative to the chassis. However, if the vehicle is involved in a crash or in some extreme driving conditions, very large forces can be applied to the mount due to movement of the engine relative to the chassis, and it is desirable to provide additional restraint on the movement of the boss relative to the cup to prevent excessive movement of the engine. It is therefore known to provide a strap, usually of braided steel or wire, which extends around the mounting device so as to pass over the boss and under the cup to provide a restraint on the total movement of the mounting device.
In the known arrangement, the strap is not fixed to the rest of the mounting device, but lies in grooves where it is held by the force from the resilient wall interconnecting the cup and boss forcing the cup and boss outwardly away from each other, with that force being resisted by the strap.
In such arrangements, there is a risk that the strap may become loose from the mounting device, particularly during the assembly process of the vehicle on which the mounting device is used and therefore at its most general the present invention proposes that the strap is fixed to the cup and/or the boss.
Thus, the present invention may provide a hydraulically damped mounting device comprising:
first and second anchor parts connected by a first deformable wall;
a working chamber at least partially bounded by the first deformable wall;
a compensation chamber for the hydraulic fluid, the compensation chamber being bounded by a second deformable wall;
a passageway for the hydraulic fluid interconnecting the working and compensation chambers; and
a strap extending between the first and second anchor parts and fixed to at least one of said first and second anchor parts.
In such an arrangement, the first anchor part may be formed by the cup, and the second anchor part by the boss. Preferably, the strap is fixed to the corresponding anchor part by a clip fixedly secured to the strap.
In some embodiments of the present invention, the strap is fixed to the boss. Then, and appropriate clip may have a projecting part which is received in a bore in the upper surface of the boss to provide suitable engagement.
Normally, the strap forms a closed loop which extends from the clip secured to the boss around the base of the cup and back to the clip. Another possibility, however, is to provide a strap with free ends, with clips fixedly secured to the respective ends, and the clips then being secured to the boss. Such a strap may loop around the base of the cup in the same way as for a closed looped strap, but the use of two clips may make the respective ends of the straps to be fixed to different parts of the boss.
Furthermore, it is then desirable that the base of the cup has at least one deformable tang to define a slot into which the strap may be received and the tang deformed to hold the strap to the base. Preferably, there are multiple tangs, and preferably the slots open axially inwardly.
In other embodiments, the strap is fixed to the cup, again, for example, by a suitable clip. There may also be a location clip fixed to the boss which engages the strap and secures the strap to the boss. However, it is then preferable that the strap slides in such a location clip. This enables the position of the strap to be adjusted to ensure that it is symmetric about the mounting device.
Again, with the strap fixed to the cup, it is possible for the strap to be a closed loop, or for the strap to be formed by strap parts with free ends extending from the clip, with those free ends then being secured to the boss either by fixed or by adjustable clips.
Guides attached to the strap may also be provided to fit to the side of the mounting device intermediate the top of the boss and the base of the cup. The guides are preferably integral with a strap. These guides distribute the load on the mounting device from the strap, and also may assist in correct positioning of the strap.
Alternatively, or in addition, resilient pads may be provided between the strap and the side of the mounting device intermediate the top of the boss and the base of the cup. Such pads may, for example, be moulded onto the flange which attaches to the clamping ring which holds the partition onto the cup. The use of such pad enables the stiffness imparted to the mounting device by the strap to be adjusted to a suitable value. It also prevents damage to the sides of the mounting device.
It is also known to mount a heat shroud on the boss, which extends over the resilient wall to reflect away from the mount heat from surrounding heat sources, such as the vehicle engine. In a development of the present invention, the orientation clip has a projection therefrom extending away from the boss onto which the heat shroud is fitable. This is advantageous since the heat shroud cannot then be fitted until the strap itself has been fitted, to prevent erroneous assembly. The orientation clip may be the clip fixed to the strap which secures the strap to the boss. Alternatively, the orientation clip may slide on the strap, for example if the strap is fixed to the cup by another clip.
The strap should be substantially inelastic. Thus, the stiffness (i.e. the force needed to achieve unit elongation) should be at least 1xc3x97106 Nmxe2x88x921, preferably at least 2xc3x97106 Nmxe2x88x921. Note that a stiffness greater than 10xc3x97106 Nmxe2x88x921 may be difficult to achieve with sufficiently light materials.